Conventional computer systems include a memory and a processor coupled to the memory, the processor including an access control arrangement which effects accesses to the memory. With respect to each access, the access control arrangement will, if necessary, delay completion of the access in the absence of and until the occurrence of a ready signal, in particular by entering successive wait states until the ready signal is received. In the case of an access to a device for which the duration of the access cannot be predicted in advance, a non-deterministic circuit is provided to handle the generation of the ready signal. With respect to an access to a device for which the necessary delay can be predicted in advance, a deterministic circuit is provided to handle the generation of the ready signal. The known deterministic circuit also has the capability to handle a processor which can carry out a burst-type access, which involves a plurality of memory accesses in rapid succession. While this known arrangement has been generally adequate for its intended purposes, it has not been satisfactory in all respects.
More specifically, there has been an increasing trend to provide computer systems in which the processor can be upgraded in terms of type and/or speed, so that the system performance can be upgraded by a user at a future time. Although a faster processor could possibly be used with a deterministic circuit designed for use with a slower processor, it would slow down the operation of the faster processor and thus vitiate much of the speed advantage desired from the processor upgrade. To date, therefore, a unique deterministic circuit has been used for each processor type and/or speed, and thus the deterministic circuit had to be changed whenever the processor was changed in order to realize optimum performance. As a result, it has become conventional to provide a special processor circuit board which plugs into a connector on the motherboard of the computer system and which carries the processor and the deterministic circuit, and possibly support circuitry such as a clock generation circuit producing clock signals at a speed corresponding to the speed of the processor. Of course, it is inconvenient, inefficient and expensive to replace an entire processor board simply to upgrade the processor.
It is therefore an object of the present invention to provide a single deterministic circuit which is sufficiently generic or flexible to work with a wide variety of processor types and speeds, so that it is not necessary to provide a separate processor board. The deterministic circuit and a socket for the processor would be provided directly on the motherboard, whereby the processor could be replaced basically by removing it from the socket and inserting a different processor in the socket, possibly with a change to a jumper or switch, and the deterministic circuit would simply be programmed during system initialization to be compatible with the particular type and speed of processor currently present in the socket.